Thursday, June 28, 2018

Season 12 superfinal, games 39-46

After 46 games Stockfish leads 10-5 with 31 draws. The draw rate continues to be low, now at 67%. Stockfish is firmly in the lead as the match approaches the halfway point.

Stockfish's eval increased over 1 after the start of game 20.1. On move 24 Stockfish went a pawn up and created a queen side passer. Komodo locked the king side and got the pawn back, evals started to come down. The white passer was stopped on the 6th rank and then the engines shuffled for a while. The engines started to exchange pawns and pieces, Komodo created a pair of central passers. Evals were 0 for a long time, the game ended with a perpetual check. In the reverse game 20.2 there were many early exchanges and the game reached a RB vs RB position on move 29. Evals came down as the engines exchanged pawns, the game was adjudicated when the evals were low enough to activate the draw rule.

Evals stayed close to 0 throughout game 21.1, despite the opening which was a King's Gambit variant. Stockfish sacrificed a knight for pawns early in the game, this removed the threat on its king. Komodo was behind in development, the engines exchanged most pieces and got a R vs BN imbalance with Stockfish 2 pawns up. On move 26 only RB vs BBN remained, Stockfish thought it had a small advantage. Komodo push a passer on the king side, after Stockfish captured it the engines shuffled until draw adjudication. The reverse game 21.2 started with a knight and bishop sacrifice by Komodo. Stockfish gave the bishop back and exchanged queens, Komodo put a rook and a passer on the 7th rank. Evals were 0 as all this was happening. On move 31 only RN vs RBN remained, and Stockfish pushed a second passer to the 7th rank. Komodo stopped a passer and traded pieces to get a knight ending and a repetition draw.

Stockfish's eval constantly increased after the start of game 22.1. All the pieces were on the board in a closed position, the first capture occured on move 35 when Stockfish went up a pawn. After a few exchanges the position became static and the engines started shuffling, Stockfish eval close to 2 and Komodo's eval close to 1. It was a bit surprising that Komodo chose to move a pawn on move 68.

Stockfish's eval jumped a level, there was another piece exchange that changed the pawn structure a little. Then the engines resumed their shuffling. The white king walked to the queen side to get away from a potential attack on the h file. Komodo was playing on increment for a long time, yet the evals remained constant. The 50-move counter reached 15 when Stockfish captured a second pawn with an eval jump, it thought Komodo finally made a mistake.

Komodo's eval started to increase very rapidly, it saw it was in trouble. Stockfish had 3 pawn breaks available on the a, e and h files and Komodo scrambled to rearrange its pieces in defense. Eventually Stockfish gave a rook for a knight, taking out an important defender and creating a queen side passer.

The white queen side pawns began to march and Komodo's defense collapsed when two connected pawns reached the 6th rank.

In the reverse game 22.2 the engines opened a file on the queen side early. Komodo's eval increased from the start and then came back down under 0.5. The engines locked the center, exchanged a few pieces and started to shuffle. Komodo avoided the 50-move draw but the game was adjudicated by the draw rule a few moves later.

The 23rd opening was only one ply long, 1.g4!!, the Grob opening. In game 23.1 evals started around negative 1 and drifted slowly downwards. Stockfish kept its king in the center uncastled. It pushed pawns on the king side, Komodo won a pawn on the queen side, both sides did not look safe for the white king. Komodo gave two pawns and created a central passer, both evals jumped over 1 while Stockfish chose to castle long.

The engines had a long PV agreement, evals slowly increased as they played the line, Komodo's passer reached the 3rd rank. The black major pieces moved to the queen side, threatening the white king. Stockfish gave a bishop to remove the passer and evals jumped over 2. After exchanging queens only RR vs RRN remained.

Komodo captured a pawn and exchanged a pair of rooks, the R vs RN ending was a win.

In the reverse game 23.2 Stockfish's eval started at 1.5 and increased steadily. Both kings stayed
in the center uncastled. Stockfish pushed pawns on the king side and Komodo sacrificed a knight for two pawns to open up the king side and
expose the black king. Stockfish's knights were very active, both with outposts on the 4th rank.

The engines played out a long line that appeared in both their PVs. After exchanging rooks Stockfish captured a pawn and created passers on the queen side. The engines exchanged queens and traded pawns until only RN vs RBN remained, Stockfish with its last pawn and its eval approaching 4.

Stockfish captured one of the white pawns, and the game was adjudicated without playing out the win. Stockfish's PV suggested that Komodo was going to lose the knight, Komodo's PV headed for a won knight ending. Both engines won this opening with black, first biased opening of the match.